1. Field of the Invention
The present invention relates to wireless communications and, more particularly, to a cell reselection method based on a priority handling in wireless communication systems and an apparatus for supporting the same.
2. Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
In wireless communication systems, a cell having narrow coverage such as a micro cell, a femto cell, a pico cell, and the like may be installed in a specific location within the coverage of the macro cell having wide coverage.
Due to a mobility of a user equipment as a mobile devices, the quality of service which is currently provided for the user equipment may be degraded or the user equipment may detect a cell that can provide better service. According, the user equipment may move to a new cell, which is called the mobility performance of the user equipment.
In a procedure for a cell reselection, the user equipment selects a target cell based on priorities of frequencies. And then, the user equipment tries to connect to the target cell by transmitting a connection configuration message. When the connection to the target cell completes, the user equipment may receive a service from the target cell.
In a certain case, the request of the user equipment may be rejected for various reasons, e.g. an overload of the target cell, and accordingly, the user equipment performs the cell reselection procedure again based on the priorities. The user equipment may select the cell that rejected the connection request, and the selected cell is still in a situation where the cell cannot provide a normal service. As a result, the user equipment repeatedly performs the cell reselection, but cannot receive any service from a network. Therefore, some mechanism to enable the network to control the cell reselection operation of user equipment may be needed, in case that the request for connection is rejected. For this, a method of lowering a priority of one or more frequencies may be considered. According to this, in the corresponding frequency, a lowest priority, that is, a lower priority which is lower than any other priority configured by the network.
In a situation that lowering priority is applied for a predetermined frequency, the user equipment may detect that a cell providing a predetermined service or that is available to provide better service is present in the corresponding frequency. In this case, a contradictory operation of the user equipment may be occurred on whether to apply the lowest priority or the highest priority to the corresponding frequency. In this situation, if the user equipment applies the lowest priority to the corresponding frequency, the user equipment may not select a cell on the corresponding frequency for a target cell through the cell reselection, as a result, the user equipment may not move to the cell that is available to provide better service.